MAGNETIC STACK INCLUDING MgO-Ti(ON) INTERLAYER

ABSTRACT

A stack includes a substrate and a magnetic recording layer. Disposed between the substrate and magnetic recording layer is an MgO—Ti(ON) layer.

RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 14/068,871 filedOct. 31, 2013, which claims the benefit of Provisional PatentApplication Ser. No. 61/884,960 filed on Sep. 30, 2013, and which arehereby incorporated herein by reference in their entireties.

SUMMARY

Embodiments discussed herein involve a magnetic stack that includes asubstrate, a magnetic recording layer, and a MgO—Ti(ON) layer disposedbetween the substrate and the magnetic recording layer.

Certain embodiments involve a stack that includes a substrate, amagnetic recording layer, a heatsink layer disposed between thesubstrate and the magnetic recording layer, and a MgO—Ti(ON) layerdisposed between the heatsink layer and the magnetic recording layer.

Embodiments are also directed to methods including depositing MgO andTiO using a composite sputtering target in a nitrogen environment toform a MgO—Ti(ON) layer. An FePt magnetic layer is then epitaxiallygrown on the MgO—Ti(ON) layer.

Further embodiments are directed to an apparatus including a sputteringtarget comprising MgO and TiO configured to deposit a MgO—Ti(ON) layerin a nitrogen sputtering environment.

These and other features and aspects of various embodiments may beunderstood in view of the following detailed discussion and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are cross sectional diagrams of magnetic stacks thatinclude MgO—Ti(ON) interlayers, according to some embodiments;

FIG. 2 is a flow diagram illustrating a process for forming anMgO—Ti(ON) interlayer, according to some embodiments;

FIGS. 3A-C show the M-H loops of interlayers with and without nitrogen;

FIG. 4 shows an X-ray diffraction graph of interlayers with varyingamounts of nitrogen;

FIG. 5 shows the signal-to-noise ratio and corresponding laser powerreduction for media with varying amounts of nitrogen in an MgO—Ti(ON)interlayer;

FIG. 6 shows the change in deposition rate of an MgO—Ti(ON) layer basedon the amount of nitrogen in the sputtering gas;

FIG. 7A shows the change in thermal conductivity based on varying targetcompositions and nitrogen flow rates;

FIGS. 7B-C are diagrams illustrating processes that can be used toproduce an MgO—Ti(ON) layer according to some embodiments;

FIG. 8A shows relative amounts of defects in sample media with an MgOinterlayer;

FIG. 8B shows relative amounts of defects in sample media with anMgO—Ti(ON) interlayer;

FIG. 9A shows laser power reduction for media with varying MgO—Ti(ON)interlayer thicknesses; and

FIG. 9B shows signal-to-noise ratios for media with varying MgO—Ti(ON)interlayer thicknesses.

DETAILED DESCRIPTION

Heat assisted magnetic recording (HAMR) has the ability to extend theareal density of magnetic recording due to the high magnetocrystallineanisotropy of the materials used in the recording layer. In order toform the HAMR media, one or more sublayers can be used to orient and/orcontrol the grain size of the high anisotropy magnetic recording layer.For example, for recording layers comprising FePt, these sublayers canbe used to induce the L1₀ (001) texture of the FePt film. Themicrostructures of FePt (or other magnetic layers) depend on sublayersimmediately below which play a role in controlling the microstructuresof the magnetic layer such as c-axis dispersion and grain size. Forexample, the sublayers may provide one or more of the followingproperties: 1) suitable lattice structure for magnetic layer epitaxialgrowth; 2) chemical stability and diffusion barrier; 3) thermalresistance and/or conductance suitable for rapid thermal transport ofheat from the magnetic layer(s) to heatsink layers; and (4) control ofthe laser power required to heat the magnetic layer(s) to the requiredrecording temperature.

HAMR media are commercially mass produced. In addition to satisfyingperformance properties mentioned above, HAMR media must withstand amass-production environment. One example of a mass-production techniqueis direct current (DC)-sputtering. DC sputtering differs from othersputtering techniques (e.g., radio frequency (RF)-sputtering) in thevoltage, system pressure, sputter deposition pattern, type of targetmaterial, deposition speeds, and low defect levels. Conventional ceramicMgO interlayers cannot be DC-sputtered. While a pulsed DC sputtering canbe used with a metallic magnesium target in a mixed oxygen and argon gasenvironment, this tends to result in high particle generation. Sublayermaterials developed and tested in a research lab environment may satisfyperformance properties; however, these materials do not necessarilyscale up to withstand commercial, mass production techniques. Forexample, sublayers comprising MgO—TiO have been suggested for use as aninterlayer. But when deposited with DC-sputtering techniques, theseMgO—TiO interlayers achieved insufficient magnetics compared to aconventional MgO interlayer, or resulted in high particle generationwhen the MgO—TiO target compositions shifted toward higher MgO content.Thus, promising performance test results for media produced in a labenvironment cannot be relied upon for media produced in a commercialenvironment.

Embodiments discussed herein involve the use of an MgO—Ti(ON) layer(hereinafter “MTON layer”) arranged in a magnetic stack between thesubstrate and the magnetic recording layer. The MTON layer may provideat least some of the properties set forth above for the magneticrecording layer. In addition to promoting the orientation of themagnetic layer epitaxial growth (e.g., FePt (001) epitaxial growth), theMTON layer can support granular two-phase growth of the magneticrecording layer. Furthermore, the MTON layer may also provide aspecified amount of thermal resistivity and/or conductivity in the stackwhile being produced by DC-sputtering with high deposition speed and lowresulting defect level.

FIG. 1A illustrates a magnetic stack 100 that includes an MTONinterlayer 130. The MTON layer 130 underlies a magnetic recording layer140 in the stack 100. As shown in FIG. 1A, the MTON layer 130 isdisposed, e.g., deposited, between the substrate 110 and the magneticrecording layer 140. A protective overcoat or lubricant layer 150 may bedisposed on the magnetic recording layer 140. The magnetic recordinglayer 140 is a granular two-phase layer. The first phase of the magneticrecording layer 140 comprises magnetic grains and the second phasecomprises non-magnetic segregant disposed between the grain boundariesof the magnetic grains. The non-magnetic segregant may comprise one ormore of C, SiO₂, Al₂O₃, Si₃N₄, BN, or another alternative oxide,nitride, boride, or carbide material. Suitable materials for themagnetic grains include, for example FePt, FeXPt alloy, FeXPd alloy,CoPt, CoXPt where X is a dopant. Although any of these materials invarious combinations may be used for the magnetic layer 140, theexamples provided herein focus on FePt as the magnetic recording layermaterial. In some configurations, the magnetic recording layer comprisesmagnetic crystalline grains of FePt and a non-magnetic segregantcomprising SiO_(x) and C disposed between the crystalline grains. Themagnetic layer may comprise SiO_(x) in an amount between about 35 andabout 45 vol. % and C in an amount of about 20 vol. %.

The interlayer 130 comprises a combination of MgO and Ti(ON)—an MTONlayer. The composition of MgO has a ratio of Mg:O=1:1 such that MgO is aline compound, and the composition of Ti:(ON) is approximately 1:1. Thecomposition of (ON) in the Ti(ON) is (O_(y)N_(1-y)) where y ispreferably 0.5<y<1, resulting in oxygen rich Ti(ON). Thus, the MTONlayer can be described as(MgO)_(x)(Ti_(0.5)(O_(y)N_((1-y)))_(0.5))_(1-x). While the ratio of MgOto Ti(ON) can vary, the MTON layer can have 20-25 vol. % MgO, andpreferably at most 20 vol. % MgO. Thus, the MTON layer can be describedas (MgO)_(x)(Ti(ON))_(1-x). The amount of MgO can be determined by themethod of deposition of the MTON layer, as discussed further below.

The MTON layer 130 is a continuous layer having a thickness from 1 to500 angstroms. Each component of the MTON layer 130, MgO, TiO, and TiNhas NaCl-type crystal structure with similar, or almost the same,lattice parameters. Their respective phase diagram data indicates, forexample, MgO can have cell parameters of approximately 0.42121 nm; TiOcan have cell parameters of approximately 0.4177; and TiN can have cellparameters of approximately 0.4239 nm. The high temperature phase oftitanium-monoxide (TiO) takes a NaCl-type crystal structure, and Ti:Oatomic ratio ranges from TiO_(0.7) to TiO_(1.25) with significant amountof vacancies in the lattice. Addition of nitrogen into those vacanciescan stabilize the NaCl-type lattice even at room temperature, at whichpure TiO loses its NaCl ordering. The stabilized NaCl-type crystal phasealso serves as a growth orientation template, or seedlayer, for themagnetic recording layer, similar to MgO and TiN.

In some embodiments, a magnetic stack 105 may include a MTON interlayer130 in conjunction with further underlayers as illustrated in FIG. 1B.FIG. 1B illustrates a stack that is similar in many respect to the stackof FIG. 1A, having a substrate 110, interlayer 130, magnetic recordinglayer 140, and overcoat 150. These layers 110, 130, 140, 150 may havecharacteristics and materials similar to layers with the same referencenumbers described in connection with FIG. 1A. FIG. 1B shows a heatsinklayer 120 as part of the stack underlayer. Heatsink layers, such aslayer 120 are used in HAMR media to facilitate thermal management sincethe heating of HAMR media has to be powerful enough to reach desiredtemperatures (at least close to the Curie point), but the cooling ratehas to be fast enough to avoid thermal destabilization of the writteninformation during the time the media cools down. Both of these issues,efficiency of the heat delivery system and fast cooling rate, aremutually competitive—the faster the cooling rate the more heating poweris required to achieve a certain temperature increase. In someconfigurations, heatsink layer 120 may comprise (200) Cu, Mo, W, ortheir alloys such as CuX.

Copper (Cu) and/or CuX (e.g., CuX, where X can be any soluble element(s)less than about 50 molecular percent), provides sufficiently highthermal conductivity to be useful for a HAMR heat sink layer. However,layers of Cu and CuX tend to grow in (111) orientation. Magnetic stacksthat include (111) heatsink layers may employ one or more additionallayers disposed on the heatsink layer that provides or resets the growthorientation for subsequent layers in the magnetic stack, e.g., themagnetic recording layer, which are grown over the heatsink layer in(200) orientation for L1₀ phases. Having (200) and (111) mixed orientedgrains in the Cu based heatsink will induce a significant surfaceroughness in the film stack, which is not preferred in a magneticrecording media application.

For surface energy considerations, body-centered-cubic (BCC) structuredheatsink materials, such as Mo and W, preferably have (110) orientationsinstead of (200). Similar to Cu based heatsinks, magnetic stacks thatinclude (200) heatsink layers may employ one or more additional layersdeposited on the heatsink layer to provide, or reset, the growthorientation for subsequent layers in the magnetic stack. Mixed orientedgrains of (200) and (110) contribute to high media roughness, which ispreferably avoided in magnetic recording media applications.

The MTON interlayer 130 in combination with heatsink layer 120 providessuitable thermal conductivity, e.g., in a range of about 80 W/m−K toabout 400 W/m−K, and additionally provides an orientation template thatproduces a magnetic recording layer having a lower roughness whencompared to magnetic recording layers grown on non-(200) orientedheatsink layers.

In addition to the heatsink layer 120, the stack 105 can include seedand/or adhesion 112 layers disposed between the substrate 110 and theheatsink layer 120. For example, an adhesion layer 112, e.g. a tantalumlayer, having a thickness of about 3.5 nm, may be disposed on thesubstrate to promote adhesion between the substrate and an adjacentlayer. The adhesion layer 112 is used to reduce the potential fordelamination of the substrate from the rest of the stack. The stack mayinclude a seed layer disposed over the adhesion layer 112, where theseed layer initiates appropriate growth orientation for the layersabove.

The stack 105 can also include a soft magnetic underlayer (SUL) 118arranged to function as a return path for magnetic flux produced by themagnetic write field during a write operation. The SUL 118 is disposedbetween the substrate 110 (and seed/adhesion layers, if present) and theheatsink layer 120. The SUL 118 may comprise amorphous and/orcrystalline materials may have a thickness of from about 5 nm to about500 nm, or even 1,000 nm. For example, the SUL 118 may be made of anysuitable material such as CoFe, FeCoB, FeAlN, FeAlSi, NiFe, CoZrNb, orFeTaN. The SUL 118 may also comprise laminated structures and/or maycomprise antiferromagnetically coupled (AFC) SUL layers.

A magnetic stack comprising at least a MTON interlayer and a magneticrecording layer is produced as disclosed in the flow chart of FIG. 2.Prior to forming the MTON layer, a substrate is processed and optionalunderlayers are applied such as an adhesion layer, a soft magneticunderlayer, and/or one or more heatsink layers. These are fabricatedusing standard techniques known in the art and are not discussedfurther. To form the MTON layer, MgO and TiO are sputter deposited in anitrogen environment 210.

According to embodiments described herein, the MTON layer is depositedby DC-sputtering a composite target comprising MgO and TiO usingmagnetron sputtering at elevated temperature (400° C. or above). Whilevarious sputtering techniques may also be used, DC-sputtering ispreferred due to the higher deposition rates (throughput rates)achievable as compared with, e.g., RF-sputtering. DC-sputtering alsoresults in lower chamber contamination. For the disclosed embodiments,RF-sputtering is not required. The amount of MgO in the composite targetcan be determined by the sputtering technique. For example, for DCand/or pulsed DC-sputtering, the composite target includes at most 20-25vol. % MgO. The DC-sputtering occurs in a nitrogen environment such thatthe sputtering gas includes both an inert gas such as argon as well asnitrogen. The amount of nitrogen is varied via the flow rate, asdiscussed further below.

Since MgO, TiO, and TiN each have NaCl-type crystal structure, withcomparable cell parameters, the resulting MTON layer maintains theNaCl-type crystal structure. This crystal structure enables growth of amagnetic recording layer on the stack 220. An FePt (001) epitaxiallygrown layer is fabricated on the deposited MTON layer. The FePt is amagnetic recording layer that can be directly grown on the MTON layer oradditional interlayers may intervene. The stack can include furtherlayers, such as a multi-layer magnetic recording layer and protectiveovercoat layers.

As discussed above, the MTON interlayer is fabricated in a nitrogenenvironment resulting in the interlayer including nitrogen in the formof Ti(ON). Previous interlayers did not include nitrogen and insteadconsisted of MgO—TiO. However, these previous interlayers did notachieve the necessary magnetics when DC-sputter deposited. The vacancycontaining TiO tends to disassociate into metallic Ti and higher orderedTi-oxides such as TiO₂ and Ti₂O₃ upon media fabrication. Diffusion ofmetallic Ti into the FePt recording layer degrades the magneticperformance as compared with media containing a ceramic MgO interlayer.Additional impurities of higher ordered Ti-oxides, such as TiO₂ andTi₂O₃, contribute to the defect generation as particles. Presence ofinsulating impurities inside a composite MgO—TiO target, and also,presence of oxygen inside the sputtering gas environment, furtherincreases particle generation during the deposition process. Thus, mediacontaining the previous interlayers fabricated with DC-sputtering wereinsufficient.

The nitrogen reactive sputtering of the disclosed embodiments stabilizesthe crystal phase of the deposited layer by adding TiN to form aninterlayer comprised of MgO—TiO—TiN. While a layer comprising MgO—TiNcan be fabricated, the MgO content necessary exceeds 50 vol. % such thatthe film fabrication requires RF-sputtering. Thus, oxygen in the formTi(ON) enables sputtering in DC.

FIGS. 3A-3C illustrate the change in magnetics as a result of addingnitrogen to the interlayer, with a ratio of MgO:TiO=1:1 in the compositetarget. First, FIG. 3A illustrates an M-H hysteresis loop for a mediumhaving an interlayer DC-sputtered in an argon-only environment. Themedium of FIG. 3A had a measured coercivity of about 24.6 kOe. FIG. 3B,however, illustrates the M-H hysteresis loop for a medium fabricatedunder approximately the same conditions, with an exception being thatthe sputtering environment for the interlayer included nitrogen at aflow rate of 2 standard cubic centimeters per minute (sccm). Theaddition of nitrogen improved the FePt texture, as illustrated by theimproved width of the hard access opening of the M-H loop of FIG. 3B.The medium of FIG. 3B had a measured coercivity of about 38.6 kOe. TheM-H loop of FIG. 3C is similar to that of FIG. 3B since the medium wasfabricated under similar conditions with the exception being anincreased flow rate of nitrogen to 4 sccm during deposition of theinterlayer. The coercivity of the medium of FIG. 3C was measured to alsobe slightly higher at 38.9 kOe.

The improvement in magnetics and FePt texture can also be detected inthe X-ray diffraction graph of FIG. 4. FIG. 4 is a conventionaltheta-2theta scan in the 20-70 degree range with a vertical axis ofcount/sec for samples with varying amounts of nitrogen in the respectiveinterlayers. The FePt 001 and 002 peak intensities at 24 degrees and at48 degrees change with the amount of nitrogen in the sample'sinterlayer. The results for the sample containing no nitrogen in theinterlayer are identified by reference numeral 410. The 001 FePt signalis significantly weaker when compared with the samples containingnitrogen. The nitrogen in Ti(ON) serves to stabilize the NaCl phase evenunder the high speed/power density DC-sputtering conditions used tofabricate perpendicular magnetic recording media. The degree ofnitridation for the deposited interlayer is controlled by varying theAr:N₂ gas ratio in the sputtering environment. Alternatively, a desirednitrogen interlayer composition could be controlled with MgO—Ti(ON)sputtering targets. For example, the composition could be optimizedbased on the raw Ti:O ratio in TiO. In order to add nitrogen to theinterlayer composition, varying ratios of nitrogen to argon in thesputtering environment were tested.

FIG. 5 illustrates both the signal to noise ratio (eSNR) and reductionin laser power (LP) for media samples with interlayers deposited withvarying amounts of nitrogen in the sputtering environment. Each medium(disk) is evaluated with respect to reference media, which isrepresented by the zero point on the left y-axis. The closer the disktests to the reference media (more positive numbers), the resultsrepresent improved eSNR.

Also shown on the right y-axis, is the reduction in laser power toattain optimum eSNR. For example, reference media is represented by 100%laser power so a measurement of 75% LP means that laser power can bereduced by 25% to achieve optimum eSNR for a sample disk. FIG. 5illustrates that eSNR stays close or slightly above the reference mediafor nitrogen added interlayers (MTON interlayers) with approximately 25%reduction in laser power. In HAMR recording, laser power reductionduring a writing operation indicates the presence of a thermal resistor,which limits the heat flow into the film layers of the recording medium.Reduced laser power is a preferred factor in improving the reliabilityof HAMR heads—generally lower laser power will prolong the operationallife of a HAMR head.

The introduction of nitrogen into the sputtering environment alsoreduces the deposition rate of the MTON interlayer. FIG. 6 illustratesthe interlayer film growth rate for media samples with interlayersdeposited with varying amounts of nitrogen in the sputteringenvironment. As can be seen, the deposition rate changes in apredictable manner with increasing amounts of nitrogen in the sputteringenvironment regardless of the target composition. For example, targetswith ratios such as MgO:TiO=40:60, 50:50, and 20:80 (different targetcompositions are represented by differently shaped data points) bothexperience decreases in film growth rate with nitridation. In contrast,without nitrogen the film deposition rates for the same targets varyunpredictably. In addition, the change in the deposition speed up toabout 20% nitrogen in the sputtering gas changes the degree ofnitridation in Ti(ON) in the interlayer. However, highly oxidized phaseslike TiO₂ and Ti₂O₃ should not be present in the interlayer TiO. Thehighly oxidized phases are insulating and create additional particlesources in the sputtering process resulting in additional defects in themedia.

Changing the nitrogen flow rate can also influence the thermalconductivity of an MTON interlayer. FIG. 7A presents the thermalconductivity change of the interlayer with two different MgO:TiO targetratios and varying nitrogen gas flows during reactive sputtering. Thelayer conducts heat laterally in the layer as well as vertically, awayfrom the magnetic recording layer. In the interlayers with higher TiOcomposition, the left side of the figure, the change in thermalconductivity with and without nitrogen is over 50%. Thus, the thermalflow in a HAMR media stack can be tuned through selection of the MgO:TiOratios in the sputtering target and through the amount of nitrogen inTi(ON). Both factors are controlled during fabrication of the MTONinterlayer in a DC-sputtering process.

The DC-sputtering process is described further with respect to FIGS.7B-C. The two primary variables in depositing an MTON interlayer are thecomposition of the MgO—TiO target and the amount of nitrogen in thesputtering gas. With respect to the composition of the target, the ratioof MgO to TiO can vary. Different example ratios are 20:80, 40:60, and50:50. However, for MTON layers as disclosed herein, it is preferredthat the composition of the target comprise at most 20 vol. % MgO. SinceTiO has a composition range providing NaCl-type crystal structure, theTi:O ratio can vary. The Ti:O composition can vary due to the raw TiOmaterial and/or the target fabrication process. Table 1 illustrates theproperties of sample targets with varying MgO:TiO composition ratios.

TABLE 1 Material Comp. MgO 70:30 60:40 50:50 30:70 TiO Resistivity mΩcm∞ 1.8 0.72 0.52 0.4 0.31 Thermal W/m/K 59 39 34 24 13 8.3 ConductivitySputter rate nm/min 0.6 1.9 1.9 1.9 2.1 2.4 Crystal Structure NaCl NaClNaCl NaCl NaCl + TiO TiOBased on the above properties, DC-sputtering can be used with each ofthe targets, except that of the left-most column. MgO cannot beDC-sputtered alone. While it is possible to use the targets with ahigher MgO content (example 70% and 60%) with a DC-sputtering technique,it is not preferred.

With respect to the amount of nitrogen in the sputtering gas, asdiscussed above, the amount is controlled by varying the flow rate ofnitrogen during DC-sputtering. FIG. 7B illustrates an approach togrowing the MTON layer that includes sputtering MgO—TiO in the presenceof N₂ to achieve the MTON interlayer in accordance with someembodiments. In step 1, argon at 24 standard cubic centimeters perminute (sccm) and N₂ at 16 sccm flow into the sputtering station for 2seconds prior to commencement of sputtering. In step 2, MgO—TiO is DCsputtered for 16 seconds at 0.5 kW. Note that although DC sputtering isused in the examples discussed herein, AC or RF sputtering are alsosuitable for deposition of the MTON layer. During step 2, both of theargon and N₂ flows are kept the same as in step 1. In step 3, the argonflow rate is reduced to 5 sccm and the N₂ flow is turned off. Theapproach of FIG. 7B provides an interlayer that includes MgO—TiO—TiN,e.g., (MgO)_(x)(Ti_(0.5)(O_(y)N_((1-y)))_(0.5))_(1-x). The amount ofoxygen in the deposited layer influences the wetting, and resultingorientation control, of the subsequent FePt layer. Also, the addition ofnitrogen to the deposited layer provides for finer grains in thesubsequent FePt layer, as compared with an interlayer without nitrogen.Varying the flow rates and target compositions provides for a comparisonof sample media with an MTON interlayer with desirable magnetics. Forexample, a medium with a positive deviation in SNR and a laser powerreduction of approximately 25% satisfies certain requirements for HAMRrecording.

FIG. 7C illustrates another approach to growing the MTON layer thatincludes sputtering MgO—TiO in the presence of N₂ to achieve the MTONinterlayer in accordance with some embodiments. In step 1, argon at 150sccm and N₂ at 10 sccm flow into the sputtering station for 1 secondprior to commencement of sputtering. In step 2, MgO—TiO is DC sputteredfor 8.5 seconds at 0.6 kW. Note that although DC sputtering is used inthe examples discussed herein, AC or RF sputtering are also suitable fordeposition of the MTON layer. During step 2, both of the argon and N₂flows are kept the same as in step 1. In step 3, the argon flow rate isreduced to 5 sccm and the N₂ flow is turned off. The approach of FIG. 7Cprovides an interlayer that includes MgO—TiO—TiN, e.g.,(MgO)_(x)(Ti_(0.5)(O_(y)N_((1-y)))_(0.5))_(1-x).

In addition to depositing the desired layer(s), sputtering processesgenerate extraneous particles. These particles result in defects infabricated recording media. As fabrication processes improve, thesedefects are being reduced, e.g., from the 10,000's to less than 100.Historically, the majority of the particles (90+%) analyzed in samplemedia resulted from the sputtering of a conventional MgO interlayer.FIG. 8A illustrates the number of particles (˜100-200) in media sampleshaving a pulsed DC conventional MgO interlayer. Improvements insputtering processes have included target and shield improvements,fabrication in smaller batches (e.g., 100 disks at a time), and improvedstability with process control. However, the pulsed DC technique stillyields approximately 150 particles per data zone. In contrast, FIG. 8Billustrates the number of particles in media samples with a DC-sputteredMTON layer. Using perpendicular magnetic recording-like source andshield configurations, the MTON layered samples yielded fewer defects(e.g., <100 particles). Moreover, the majority of particles analyzedresulted from the composite FePT targets with only a few particlesresulting from deposition of the MTON layer.

In addition to a reduction in particles, the DC-sputtered MTON layer hasa thickness dependence on laser power and SNR. FIGS. 9A and 9Billustrate these respective relationships. For example, FIG. 9Aillustrates that as the thickness of the MTON interlayer increases, thelaser power is further reduced. Thus, the thickness of the MTON layerinfluences the thermal conductivity of a recording medium. FIG. 9B showsthat SNR improves with increasing thickness, at least up to a certainpoint. Corresponding data points 910 and 920 indicate a preferredcombination of improved SNR with reduced laser power at a thickness ofabout 22 nm. Conventional MgO interlayers exhibited little thicknessdependence on these properties; therefore, such media included at leasta second heatsink layer. With the thickness dependence exhibited by MTONinterlayers in the described embodiments, such a heatsink layer may notbe necessary.

As discussed above, the reduction in laser power exhibited by the MTONlayer indicates that the MTON layer is a thermal resistor. As opposed toceramic MgO interlayers, the required laser power for recording varieswith the MTON thickness. The presence of the MgO/heatsink interfacedetermined the laser power in the MgO interlayer instead of the MgOthickness. Therefore, the MTON interlayer exhibits a bulk resistanceinstead of an interfacial resistance as found with ceramic MgOinterlayers. The MTON layer works to both determine the orientation ofthe FePt layer (e.g., as a seedlayer) and to confine heat as a secondheatsink layer. The MTON layer can be tuned based on the compositionand/or thickness of the layer.

It is to be understood that even though numerous characteristics ofvarious embodiments have been set forth in the foregoing description,together with details of the structure and function of variousembodiments, this detailed description is illustrative only, and changesmay be made in detail, especially in matters of structure andarrangements of parts illustrated by the various embodiments to the fullextent indicated by the broad general meaning of the terms in which theappended claims are expressed.

What is claimed is:
 1. A stack, comprising; a substrate; a magneticrecording layer; and an MgO—Ti(ON) layer disposed between the substrateand the magnetic recording layer, wherein the Ti(ON) content sputteredis at least 30 vol. %.
 2. The stack of claim 1, wherein the MgO—Ti(ON)layer has NaCl-type crystal structure.
 3. The stack of claim 1, whereingrowth orientation of the magnetic recording layer is based on theMgO—Ti(ON) layer.
 4. The stack of claim 1, wherein the MgO—Ti(ON) layeris a (MgO)_(x) (Ti(ON))_(1-x) layer.
 5. The stack of claim 1, whereinthe MgO—Ti(ON) layer is a (MgO)_(x)(Ti_(0.5)(O_(y)N_((1-y)))_(0.5))_(1-x) layer.
 6. The stack of claim 1,wherein a thickness of the MgO—Ti(ON) layer determines an amount oflaser power applied to heat the stack.
 7. The stack of claim 4, whereinthe composition (x) of the (MgO)_(x) (Ti(ON))_(1-x) layer determinesthermal conductivity of the stack.
 8. The stack of claim 5, wherein thenitrogen content (1-y) of the (MgO)_(x)(Ti_(0.5)(O_(y)N_((1-y)))_(0.5))_(1-x) layer determines an amount oflaser power applied to heat the stack.
 9. The stack of claim 1, whereinthe MgO—Ti(ON) layer comprises about 70 vol. % MgO.
 10. The stack ofclaim 1, wherein the MgO—Ti(ON) layer laterally conducts heat in thestack.
 11. The stack of claim 1, wherein the MgO—Ti(ON) layer is acontinuous layer.
 12. A stack, comprising; a substrate; a magneticrecording layer; a heatsink layer disposed between the substrate and themagnetic recording layer; and a MgO—Ti(ON) layer disposed between theheatsink layer and the magnetic recording layer, wherein the Ti(ON)content sputtered is at least 30 vol. %.
 13. The stack of claim 12,wherein growth orientation of the magnetic recording layer is based onthe MgO—Ti(ON) layer and the MgO—Ti(ON) layer laterally conducts heat inthe stack.
 14. The stack of claim 12, wherein the MgO—Ti(ON) layercomprises about 70 vol. % MgO.
 15. The stack of claim 12, wherein theMgO—Ti(ON) layer is a (MgO)_(x) (Ti(ON))_(1-x) layer.
 16. The stack ofclaim 12, wherein the MgO—Ti(ON) layer is a (MgO)_(x)(Ti_(0.5)(O_(y)N_((1-y)))_(0.5))_(1-x) layer.
 17. A method, comprising:depositing MgO and TiO using a composite sputtering target, wherein thecomposite sputtering target comprises at most 70 vol. % MgO, in anitrogen environment to form a MgO—Ti(ON) layer; and epitaxially growingan FePt magnetic layer on the MgO—Ti(ON) layer.
 18. The method of claim17, wherein the MgO—Ti(ON) layer is deposited using DC-sputtering. 19.The method of claim 17, further comprising forming a heatsink layer,wherein the MgO—Ti(ON) layer is a thermal resistor formed on theheatsink layer.
 20. The method of claim 17, wherein the MgO—Ti(ON) layeris deposited in less than 10 seconds.